In the oil and gas industry and as described, for example, in International patent application WO 2011/146353, a wide variety of systems are known for producing fluids from a subterranean formation.
Oil wells typically rely on natural gas pressure to propel crude oil to the ground surface. In formations providing sufficient pressure to force the fluids to the ground surface, the fluids may be collected and processed without the use of artificial lifting systems.
Oftentimes, particularly in more mature oilfields that have diminished gas pressure or in wells with heavy oil, this pressure is not sufficient to bring the oil out of the well. In these instances, the oil is pumped out of the wells using a pumping system.
At the present time, wide use is made of a pumping system including electrical submersible pumps (ESPs) disposed downhole within a well to pump the desired fluids to the ground surface. A submersible pump is usually deposited within the production fluids to then pump the desired fluids to the ground surface by generating a pressure boost sufficient to lift production fluids even in deep water subsea oil wells.
A submersible pumping system is disclosed by the above-mentioned WO 2011/146353 which states that, typically, the subterranean environment presents an extreme environment having high temperatures and pressures.
Temperatures of a subterranean environment can reach 200° C., and the pressures are of about 200-250 bar, but in some cases even up to 800 bar.
Further, fluids containing one or more corrosive compounds, such as carbon dioxide, hydrogen sulfide, and/or brine water, may also be injected from the surface into the wellbore (e.g., acid treatments). These extreme conditions can be detrimental to components of the submersible pumping system and particularly to the internal electrical components of the electric cable.
Specifically, electrical cables for submersible pumping systems typically contain a cable core comprising a metallic conductor (e.g., a copper conductor) and a polymer layer surrounding the metallic conductor which must be protected from the corrosive effects of the well fluids that surround the cable.
To protect the electrical cables, it is known in the art to provide an outer armor containing the cable core at a radially outer position with respect to the cable core itself.
Generally, this outer metal armor comprises a galvanized carbon steel tape wound according to short-pitch helical windings around the rubber protective sheath which surrounds the cable cores. The windings are engaged with each other by the fitting together of projections and recesses. This winding configuration is herein referred to as “interlocked”.
In such a way, the outer metal armor aims at protecting the insulated conductors from impact and abrasion and at protecting the cable cores against corrosive compounds in the well, while maintain a flexibility suitable for the application.
The already mentioned WO 2011/146353 teaches to protect the electrical cables by providing the cable with at least one strength member layer bonded to the cable core, the at least one strength member layer comprising a plurality of polymer-bonded strength members. The material used for the strength members of the polymer-bonded strength members may be selected from galvanized improved plow steel of different carbon content, stainless steel, aluminum-clad steel, anodized aluminum-clad steel, high strength galvanized carbon steel and/or any other suitable strength material. The material used for the polymer material encompassing the polymer-bonded strength members may be selected from a modified polyolefin, for example, amended with one of several adhesion promoters.
International patent application WO 2015/004597 teaches to protect the carbon steel elongated elements (strips or tapes) of a mechanical armor structure of a submarine flexible pipe by coating these elongated elements with an aluminum cladding.
According to this reference, the aluminum cladding of each of the elongated elements preferably has a thickness not lower than about 250 μm, more preferably of between about 250-900 μm so as to have an expected pipe working life greater than 20 years, up to 40 years.
The aluminum cladding is applied by any of the following processes: immersion in melted aluminum, coating with aluminum thin foil, flame and/or plasma spraying, aluminum extrusion.
Saakiyan, L. S. et al., Materials Science, Vol. 29, No. 6, 1993, p.600 discloses a model for describing the decrease in tensile strength of carbon steel specimens under the action of an hydrogen sulfide environment.
According to this reference, aluminum and aluminum-oxide coatings considerably increase the conventional limit of hydrogen sulfide cracking of steel parts and their operating lifetime. More specifically, coating steel with aluminum is said to increase the conventional limit of hydrogen sulfide cracking by 3.5-4 times if the thickness of the aluminum layer is 50 μm. An increase in the thickness of the aluminum layer results in a further increase in the limit of hydrogen sulfide cracking.